Charge structure and lightning sensitivity in a simulated multicell thunderstorm

Abstract

A three-dimensional dynamic cloud model is used to investigate electrification of the full life cycle of an idealized continental multicell storm. Five laboratory-based parameterizations of noninductive graupel-ice charge separation are compared. Inductive (i.e., electric field-dependent) charge separation is tested for rebounding graupel-droplet collisions. Each noninductive graupel-ice parameterization is combined with variations in the effectiveness of inductive charging (off, moderate, and strong) and in the minimum ice crystal concentration (10 or 50 L-1). Small atmospheric ion processes such as hydrometeor attachment and point discharge at the ground are treated explicitly. Three of the noninductive schemes readily produced a normal polarity charge structure, consisting of a main negative charge region with an upper main positive charge region and a lower positive charge region. Negative polarity cloud-to-ground (CG) flashes occurred when the lower positive charge (LPC) region had sufficient charge density to cause high electric fields. Two of the three also produced one or more +CG flashes. The other two noninductive charging schemes, which are dependent on the graupel rime accretion rate, tended to produce an initially inverted polarity charge structure and +CG flashes. The model results suggest that inductive graupel-droplet charge separation could play a role in the development of lower charge regions. Noninductive charging, on the other hand, was also found to be capable of producing strong lower charge regions in the tests with a minimum ice crystal concentration of 50 L-1. Copyright 2005 by the American Geophysical Union.